Excellent very sharp moon shot - thanks for posting.Taken with the 1.4x or 2x TC or both together?Is there enough detail in the image to enlarge/crop further - to show some crater detail?Would one get the same detail with same lens but with say a 550D?

FarQinell

Thanks for the extra image.Just shows that you have a remarkable lens here.Although about the same weight as the 600/4 and the 800/5.6 the extra f stop and shorter length of the 400/2.8 should make it easier to handle than the other two behomoths!!!!